In many applications, it is desired to bend sheet stock of metal or other bendable material to form a desired design. For example, a continuous sheet of metal can be bent to form the side wall of an irregularly shaped housing. One application of the present invention is in forming lighted letters, words or other designs in the sign industry. In this regard, a lighted letter is commonly formed by placing a light or lights within a three-dimensional letter-shaped housing. Typically, such a housing comprises a flat two-dimensional back plate which may be a portion of the sign surface or a separate., letter-shaped plate; a front, transparent or translucent letter-shaped plate; and a metal side wall or strip which extends about the outer and/or inner periphery of the letter. The side strip thus provides the housing with a depth sufficient to house the light or lights.
Several parameters must be considered in bending sheet stock into a predetermined design. These parameters include the longitudinal positioning of the bends on the sheet stock, the shape of the bends, and the sequence in which to make the bends. As used herein, the term "shape" includes the total angle of a corner or curve, the radius of curvature of a curve, and other bend characteristics. The material and thickness of the sheet stock may also need to be considered in forming the design. A letter can be formed from a length of sheet stock by forming a series of bends, e.g., corners or curves of appropriate shape at the appropriate positions on the sheet stock. In practice, depending upon the equipment used to form the bends, curves may be formed by a series of chord-like flat surfaces rather than one continuously curved surface.
Upon consideration, it will be appreciated that selecting a sequence for making the bends is problematic. For example, in bending a side strip to form a letter housing, the bends cannot necessarily be made in the same sequence as they would be in writing the letter. This is because such a sequence might result in mechanical interference between the already bent portions of the stock and the remaining, as yet unbent, portions of the stock or the machinery used to bend the sheet stock. That is, such a sequence might result in the unbent portion of the stock coming into contact with the bent portion or a machine. Such interference can often be avoided by selection of a suitable sequence for making the bends.
Heretofore, the process of bending a side strip for a letter shaped housing design has typically required the skill of an experienced operator. Commonly, such an operator would physically measure an associated front or back plate of the housing and use the measurements to determine the shapes and positions of the bends. Thereafter, the operator could often determine an acceptable sequence by drawing on experience and skill or through a trial and error process. The operator could then attach instructions regarding the positions, shapes and sequence of the bends directly to the side strip. For example, the instructions might be written on the stock or on tape which would be attached to the stock. Machinists would then use the instructions in making the bends.
Such manual processes have a number of drawbacks. First, as stated above, such manual processes typically require the skill of an experienced operator to perform measurements, determine an acceptable sequence for making the bends, and provide instructions regarding the positions, shapes, and sequence of the bends. In addition, such manual processes are generally time consuming, thereby increasing the cost of producing side strips. Moreover, such manual processes are often inexact and highly susceptible to error. Thus, manual processes can be inefficient, costly, and inaccurate.
A number of computer numeric controlled machines for bending metal are known. However, these machines do not determine the positions, shapes, and sequence of bends for forming sheet stock into a predetermined design and print instructions such that instructions for each curve are placed at the corresponding position on the sheet stock. Such machines are thus not adapted for incorporation into processes such as the sign industry side strip process described above.